Fuel pump runs as soon as the battery cable is hooked up! PLEASE HELP

mcglsr2

Well-Known Member
SN95 Supporter
Joined
Jul 4, 2011
Messages
3,410
Reaction score
40
Location
Orlando
Where does the fuel cut off/inertia switch come int on the schematic? Is it the very last thing before the pump?

Test for power at the fuse, and at the inertia switch.

Inertia cutoff is very last thing before the fuel pump.

The full route for power is:
Batt --> Fuse --> CCRM Fuel Pump Relay --> Inertia cutoff --> Fuel Pump.

The PCM enters the picture by controlling the CCRM Fuel Pump Relay.
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
So I had a professional electrician buddy look at the wiring diagram for my car. He said the only way the fuel pump could run with the fuse out is the fuel pump monitor circuit is back feeding power to the pump. That makes sense looking at the diagram and might explain why the old CCRM smoked since that circuit isn't designed for the full draw of a fuel pump. It looks like pin 8 on the CCRM feeds the fuel pump monitor circuit but why would it be feeding power with the key in my pocket?
 

mcglsr2

Well-Known Member
SN95 Supporter
Joined
Jul 4, 2011
Messages
3,410
Reaction score
40
Location
Orlando
So I had a professional electrician buddy look at the wiring diagram for my car. He said the only way the fuel pump could run with the fuse out is the fuel pump monitor circuit is back feeding power to the pump. That makes sense looking at the diagram and might explain why the old CCRM smoked since that circuit isn't designed for the full draw of a fuel pump. It looks like pin 8 on the CCRM feeds the fuel pump monitor circuit but why would it be feeding power with the key in my pocket?

Um, did you not see my post here?

Are you sure it's pin 8 on the CCRM? You have confirmed this on your year wiring diagram? I don't believe that is correct according to my manual, though I have a different year car, so perhaps it changed from year-to-year (and I will confirm tonight when I get home as I am at work). I honestly don't know without seeing a wiring diagram for your year. Also, the monitor "informs" the EEC - it is not directly responsible for supplying power to the fuel pump relay.

How do you know pin 8 is supplying power with the keys in your pocket? Did you probe with a multimeter? (And keep in mind pin 8 on the CCRM may not be what you think it is, so maybe it's normal for this circuit to have power.)

Lastly, I would be surprised if your new pump is the sole reason the CCRM burned up. I seriously doubt this - the fuel pump is protected by a 20 Amp fuse, if your pump was drawing more current than that, it would have popped the fuse. If your CCRM was fried *and* the fuse popped, then yes, your pump might have done it. The Aeromotive unit, at 1 atmo, is probably drawing around 11 Amps (source). Your stock wiring is certainly up to that task. Now, if you were pushing 30 lbs of boost and asking the pump to supply the fuel, *THEN* maybe your wiring isn't quite large enough (but even then the pump would be drawing around 17 Amps, still within the limits as set by Ford via a 20 Amp fuse). Certainly for KOEO, your wiring is fine.

Unless your pump is defective, something else is your problem.


Edit: and for reference, I too have the wiring diagrams for my car, as well as the service manuals (FSMs = Factory Service Manuals). I use them quite often. So while the info I provide may be specific to my car - I can't know for your car because I only have the manuals for my year - I am certainly not pulling them out of my ass. I know how to read wiring diagrams. I do this often. Sometimes I am even good at it ;)
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
Thanks for all your guidance, I'm agreeing with you and think something else is the problem.
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
So what should this be plugged into?

f461db4372b91f635b6b2463ca2b106f.jpg
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
Okay, so this is how the fuel pump is wired in my 95 5.0 - I imagine yours is similar, if not the same.

Batt --> Fuel Pump Fuse --> CCRM Fuel Pump Relay. The CCRM Fuel Pump Relay is normally open, unless the PCM (EEC) energizes the relay (the pin on the EEC is 22). Once the EEC energizes the CCRM Fuel Pump Relay via pin 22, it closes the relay, so then CCRM Fuel Pump Relay --> Inertia Cut Off --> Fuel Pump.

So. If you connect the battery and Fuel Pump comes on, then the issue is 1 of 3 things (or perhaps some combination) - and to troubleshoot, keep the harness to the Inertia cutoff unplugged so that your pump doesn't run:

1) The CCRM is bad, the Fuel Pump Relay has failed Closed - only possible if the contacts inside have "welded" themselves together
-- You can check this by connecting the battery and probing pin 5 on the CCRM - if you have voltage, that means the CCRM Fuel Pump Relay is closed, and passing voltage from the battery. If you get voltage, also check #2 below

2) The PCM (EEC) is bad - it's sending power on pin 22 when it shouldn't.
-- You can check this by checking pin #22 on the PCM (or, pin #18 on the CCRM). If there is voltage, then the EEC is sending the signal to the CCRM Fuel Pump Relay to close.

3) You have a short in your wires. The short will either be between the PCM (pin #22) and the CCRM (pin #18), tricking the CCRM into energizing the fuel pump; AND/OR between the CCRM (pin #5) and the Inertia cutoff switch.
-- You can use a multimeter to test

BONUS: there's also one more pin on the PCM to check, pin #8 - this is the fuel pump monitor. When the CCRM Relay is closed and passing voltage to the pump, this pin will also have voltage. It's possible that if the PCM energizes this pin as well, it will run your pump.

Your problem is in one or more of the places I listed. There is no where else it could be, if your wires truly are stock. If someone has run different wires without your knowledge (like a previous owner), then it's a different ball game.

Edit: this is based on my 95 GT. I don't know what you have, but if it's a 94/95 GT 5.0 then it will be the same for you. If you have a different year, it might be slightly different - but probably similar.

So I have power on pin 5 of the CCRM and pin 18 of the CCRM so it looks like the PCM is telling the relay to close which is why the pump is running. Now how do I determine if my PCM is bad or a have a short?
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
Okay, so this is how the fuel pump is wired in my 95 5.0 - I imagine yours is similar, if not the same.

Batt --> Fuel Pump Fuse --> CCRM Fuel Pump Relay. The CCRM Fuel Pump Relay is normally open, unless the PCM (EEC) energizes the relay (the pin on the EEC is 22). Once the EEC energizes the CCRM Fuel Pump Relay via pin 22, it closes the relay, so then CCRM Fuel Pump Relay --> Inertia Cut Off --> Fuel Pump.

So. If you connect the battery and Fuel Pump comes on, then the issue is 1 of 3 things (or perhaps some combination) - and to troubleshoot, keep the harness to the Inertia cutoff unplugged so that your pump doesn't run:

1) The CCRM is bad, the Fuel Pump Relay has failed Closed - only possible if the contacts inside have "welded" themselves together
-- You can check this by connecting the battery and probing pin 5 on the CCRM - if you have voltage, that means the CCRM Fuel Pump Relay is closed, and passing voltage from the battery. If you get voltage, also check #2 below

2) The PCM (EEC) is bad - it's sending power on pin 22 when it shouldn't.
-- You can check this by checking pin #22 on the PCM (or, pin #18 on the CCRM). If there is voltage, then the EEC is sending the signal to the CCRM Fuel Pump Relay to close.

3) You have a short in your wires. The short will either be between the PCM (pin #22) and the CCRM (pin #18), tricking the CCRM into energizing the fuel pump; AND/OR between the CCRM (pin #5) and the Inertia cutoff switch.
-- You can use a multimeter to test

BONUS: there's also one more pin on the PCM to check, pin #8 - this is the fuel pump monitor. When the CCRM Relay is closed and passing voltage to the pump, this pin will also have voltage. It's possible that if the PCM energizes this pin as well, it will run your pump.

Your problem is in one or more of the places I listed. There is no where else it could be, if your wires truly are stock. If someone has run different wires without your knowledge (like a previous owner), then it's a different ball game.

Edit: this is based on my 95 GT. I don't know what you have, but if it's a 94/95 GT 5.0 then it will be the same for you. If you have a different year, it might be slightly different - but probably similar.

So how can I use my multi-meter to check for a short?

I really appreciate everyone's help, I just really confused because I parked a perfectly good running car and now I have a problem that doesn't appear to have anything to do with what I was working on.
 

mcglsr2

Well-Known Member
SN95 Supporter
Joined
Jul 4, 2011
Messages
3,410
Reaction score
40
Location
Orlando
So how can I use my multi-meter to check for a short?

I really appreciate everyone's help, I just really confused because I parked a perfectly good running car and now I have a problem that doesn't appear to have anything to do with what I was working on.

Pre-step: disconnect the connector at the inertia cut-off switch (or trip the switch). Either way, you do *not* want power to reach your fuel pump at this point. Also, the key is *not* to be inserted into the ignition at any point, unless otherwise stated in a step.

I know in another post you said your CCRM had power on pins 5 and 18. Good to know, but let's table this for a minute.

Please follow the steps below, and report back on your findings.

Steps
-------------------------------

  1. Disconnect your CCRM - completely unplug it.
  2. Hook up your battery.
  3. Briefly connect the fuel pump at the inertia cut-off switch (or reset it); does the fuel pump come on?
  4. If yes, disconnect the fuel pump, then GO TO STEP 6.
  5. If no, disconnect the fuel pump, then GO TO STEP 7.
  6. You have a short. The short is between the CCRM harness (but not the CCRM itself) and the fuel pump. Somewhere, on this circuit, +12V BATT is being fed in, completely bypassing the CCRM and PCM. Finding the short will suck, and honestly may be impossible if you aren't willing to open up harnesses tracing this wire. See the ALTERNATIVE at the bottom of this post. STOP.
  7. On the CCRM harness, check the Fuel Pump Relay Input pin (pin #18 on my 95GT) for continuity to ground. One probe goes on a good ground, at the battery or engine for example. The other probe on the pin. Is there continuity?
  8. If yes, GO TO STEP 10.
  9. If no, GO TO STEP 15.
  10. Disconnect the PCM from the harness - completely unplug it. Check the Fuel Pump Relay Input pin (pin #18 on my 95GT) again for continuity. Is there continuity?
  11. If yes, GO TO STEP 13.
  12. If no, GO TO STEP 14.
  13. This is your problem - the circuit between the PCM and CCRM is being grounded. It should normally be open. A wire, somewhere, is contacting this wire and sending it to ground. You will have to follow the wire between the PCM and CCRM to locate the issue. Using the probes, check, sections of wire for continuity. If you get no continuity, that section of wire is good. If you get continuity, it is being grounded nearby - try to locate it. Once found, fix it. STOP.
  14. This means that the PCM is closing this circuit. When the PCM closes this circuit, it tells the CCRM relay to energize, and you get power to your fuel pump. If the PCM is doing this, it is most likely bad, as it should *not* be doing this (it does this with the key in the ignition and turned to ON and START positions). Easiest way to test is to borrow a known working PCM from a buddy. STOP.
  15. Unhook the battery.
  16. Reconnect the CCRM.
  17. Hook up the battery.
  18. On the CCRM harness, check the Power To Fuel Pump pin (pin #5 on mt 95GT) for voltage. Does it have voltage?
  19. If yes, GO TO STEP 21.
  20. If no, GO TO STEP 25.
  21. On the CCRM harness, check the Fuel Pump Relay Input pin (pin #18 on mt 95GT) for voltage. Does it have voltage?
  22. If yes, GO TO STEP 10.
  23. If no, GO TO STEP 24.
  24. Most likely your CCRM is bad. It is energizing the fuel pump relay when it shouldn't be. Test with a known good CCRM. STOP.
  25. This is not a possible state, as your fuel pump runs when the battery is connected. Please go back to the previous step and double check your work.

That should get you started. Please let me know what you discover.


ALTERNATIVE
-----------------

If the issue ends up being that the PCM tells the CCRM to energize at the correct time, however the wire feeding power to the pump is energized ALL the time (meaning the CCRM isn't listening to the PCM), you can bypass that circuit if you want (with the added bonus of you can now run thicker AWG wire to satisfy the demands of your larger pump). To do this, you will cut the wire from pin #5 on the CCRM harness, connect it to your own wire, and run that wire to the inertia cut-off switch, cutting the original wire. Don't forget to cut the wire at pin #8 on the PCM and run your new wire to this as well. Essentially, you are replacing the existing wire (which for some reason has +12V BATT all the time) with your own wire that is energized properly via the CCRM. If this ends up being your problem, I can be more specific with what I am talking about here if necessary.
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
1. Disconnected CCRM, pump didn't run.
2. Tested continuity on pin 18, getting 12 volts.
3. Disconnected PCM, no voltage on pin 18.
 

ttocs

Post Whore
Joined
Oct 9, 2009
Messages
32,393
Reaction score
5,560
Location
Evansville Indiana
OK your using technical electrical terms I think a little incorrectly and confusing me... you say you tested for continuity, but listed a voltage. Testing for continuity means you put one end of the meter on one end of the wire, and then the other end of the meter on the other end and it will tell you if the wire is broken or good, no voltage is measured. You can also test for continuity to ground by using one end on the ground/chassis. Often the diode test function on the meter is used for this and it will beep if its a good wire or nothing happens if its bad. So did you test for voltage, or continuity?
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
Do I need to use the ohm function on my volt meter when testing for continuity?
 

mcglsr2

Well-Known Member
SN95 Supporter
Joined
Jul 4, 2011
Messages
3,410
Reaction score
40
Location
Orlando
Do I need to use the ohm function on my volt meter when testing for continuity?

Yup, that's the guy. For the scale, pick the one that gives you something like x.xx where x is a number and the . is the decimal point. This might be like 20 Ohm (as opposed to 200 Ohm), don't remember off the top of my head.
 

ttocs

Post Whore
Joined
Oct 9, 2009
Messages
32,393
Reaction score
5,560
Location
Evansville Indiana
or the diode test. That usually has a symbol with an triangle with a line in front of it and through it. It will beep when the wire is good, and do nothing if its bad.
 
OP
OP
B

BigSkySN95

Member
Joined
Jun 21, 2007
Messages
148
Reaction score
0
Pin #5 & #18 have voltage, no continuity on pin #18. I ordered a new PCM
 

mcglsr2

Well-Known Member
SN95 Supporter
Joined
Jul 4, 2011
Messages
3,410
Reaction score
40
Location
Orlando
Pin #5 & #18 have voltage, no continuity on pin #18. I ordered a new PCM

Okay, so just to confirm, at Step #7, you measured continuity on CCRM pin #18, and got continuity, meaning 0.00 (as in not open), when touching this pin to ground.

And then at Step #10, after disconnecting the PCM, you measured continuity again on CCRM pin #18 and this time did NOT get continuity, meaning you got an open circuit.

Thus the PCM was grounding the wire when it wasn't supposed to be, thus the PCM is bad, thus you ordered a new one. Yes?
 

Latest posts

Forum statistics

Threads
77,439
Messages
1,502,159
Members
14,920
Latest member
marktuck99

Members online

Top